This proposal is to examine the mechanism of regulation of the enzyme 3-hydroxy-3-methyl glutaryl Coenzyme A (HMG-CoA) reductase in Chinese hamster ovary cells. The analysis of regulation of this critical enzyme of cholesterol biosynthesis will be performed by a combination of somatic cell genetic and biochemical techniques. Studies are proposed to examine the cis or trans nature of the dominance of regulatory mutations, to determine the chromosomal assignment of regulatory lesions in HMG-CoA reductase and the structural genes for the enzyme itself, to isolate and characterize possible pleotropic mutants missing enzymes of mevalonate biosynthesis and to isolate mutants which are gene amplified for HMG-CoA reductase. Other studies will examine the regulation of turnover of HMG-CoA reductase by measuring messenger RNA levels using in vitro translation and pulse chase radio immune precipitation studies to measure the rate of degradation of the enzyme.